Non-destructive inspection of parts has been used for many years. More recently, ultrasonic inspection has been extended to small parts such as integrated circuits or other electronic components. During the manufacture of integrated circuits (ICs), the parts are often loosely arranged in trays or holders to facilitate transfer of the parts through the production process. In order to prevent delays in the production process, an ultrasonic tester that can accommodate trays of parts is required.
An ultrasonic tester may include three sections. The first section is a de-bubbling area where the parts in the carriers are wetted and air bubbles are removed. The normal convention is to submerge the parts and ‘wiggle’ them to remove the air bubbles. The second section is a scanning station where wetted and bubble free parts are ultrasonically scanned. In order to complete the scan in a short time, the ultrasonic transducer must be moved across the parts at high speed in close proximity to the parts. The result is a motion in the fluid that tends to move the parts in the carriers or dislodge them from the carrier. The third section is a drying area, where a gas stream is used to dry any residual coupling fluid from the parts. Typically compressed and/or heated air is directed across the parts. Each of these processes tends to dislodge the parts when they are loosely arranged in a tray or carrier.
There is a continuing drive towards the use of higher frequency ultrasound, which provides greater resolution of the scanned image. Since higher frequency ultrasound is attenuated in very short distances, it is necessary to move the ultrasonic transducer very close to the object being scanned. Conventional, non-immersion, transducer may be fitted with squirters or bubbles that produce a column of coupling fluid between the transducer and the part. These do not allow the transducer to be moved close enough to the part to prevent the attenuation of very high frequency ultrasound.